AD Values Research Articles

The advertising value of Twitter Ads: a study among Mexican Millennials

Purpose – This study set out to measure the perceived Advertising Value of Twitter ads on a large sample of Mexican Millennials. Design/methodology/approach – An online survey was used to collect data among 630 university students. The hypothesized antecedents of Advertising Value were Informativeness, Entertainment, Irritation and Credibility. The model was estimated using Partial Least Squares. Findings – Results indicate Informativeness and Entertainment were the strongest predictors, with Credibility in third place. In addition, Credibility displayed gender effects: it was significant for female respondents but not for males. Irritation failed to reach statistical significance in most subsamples, suggesting Twitter ads are more acceptable to Millennials than other advertising formats. Originality/value – Millennials tend to dismiss traditional advertising formats. At the same time they are heavy users of Social Networking Sites. This research provides the first empirical estimation of the Ducoffe model of Advertising Value in the microblogging service Twitter, and the first application of this robust model of web advertising to a Latin American sample. Our results have important implications for both regional and global brands targeting Millennials.

Prognostic value of adiponectin in coronary artery disease: Role of diabetes and left ventricular systolic dysfunction

ObjectivesAdiponectin (AD) promotes insulin sensitivity and has anti-atherogenic properties. However, the role of AD on clinical outcomes in coronary artery disease (CAD) is controversial. We analyzed whether AD was an independent predictor of all-cause mortality and hospitalization in patients with CAD. MethodWe prospectively enrolled 138 patients with stable CAD, with or without type 2 diabetes and with or without left ventricular dysfunction. A telephone follow-up was conducted to register long term outcomes. Sensitivity/specificity ratio for AD was investigated with ROC analysis and the independent role of AD on outcome was evaluated with Cox regression model of analysis. The survival rate was represented by Kaplan Meyer curves. ResultsOf 138 patients, 61 had type 2 diabetes and 71 left ventricular systolic dysfunction (EF<40%). Median time of follow-up was 1384days; mortality rate was 18.8% (26 deaths) and hospitalization rate was 47.1% (65 events). Mean concentration of AD was 9.87±7.53ng/ml; the analysis of the ROC curve identified an AD cut-off level of 13.2ng/ml (AUC 0.779; p<0.0001). Patients with AD >13.2ng/ml had a significantly higher risk of death (HR=6.50; 95% CI: 2.40–17.70), but not of cardiovascular hospitalization (HR=0.87; 95% CI: 0.31–2.44). AD predictivity remained significant also in patients with type 2 diabetes and with left ventricular systolic dysfunction. ConclusionIn stable CAD, an AD value of >13.2ng/ml independently predicts a 6-fold increased risk of all-cause mortality.

Altered structural connectivity is related to attention deficit/hyperactivity subtypes: A DTI study

This study aimed to provide novel insights into the white matter (WM) microstructural properties of Attention Deficit/Hyperactivity Disorder (ADHD) subtypes by recruiting a relatively large sample of stimulant-naïve children and adolescents who had no comorbidity other than Oppositional Defiant Disorder and were homogenous according to the DAT1 gene polymorphism. A sample of 72 ADHD subjects and 24 controls aged 8–15 years were enrolled in the study. We applied tract-based spatial statistics to the DTI measures for obtaining fractional anisotropy (FA) and axial, radial diffusivity (AD, RD) measures to explore ADHD type-related differences in WM for the whole brain. Comparing ADHD-Combined group (ADHD-C) with the ADHD predominantly inattentive group (ADHD-I) we detected increased RD in several bilateral brain area and increased AD mostly in left side of the brain, including the body and splenium of the corpus callosum; the anterior and posteriors limbs of the internal capsule; the superior, anterior and posterior corona radiata; the posterior thalamic radiation; and the superior longitudinal fasciculus. Likewise, mostly in the overlapping brain areas, the ADHD-C group presented increased AD values than ADHD-RI. Significant differences among ADHD types could be a preliminary evidence that they have distinct microstructural properties. There were no significant differences in diffusivity between controls and both the ADHD group as whole or any ADHD subgroups.

Bi-directional changes in fractional anisotropy after experiment TBI: Disorganization and reorganization?

The current dogma to explain the extent of injury-related changes following rodent controlled cortical impact (CCI) injury is a focal injury with limited axonal pathology. However, there is in fact good, published histologic evidence to suggest that axonal injury is far more widespread in this model than generally thought. One possibility that might help to explain this is the often-used region-of-interest data analysis approach taken by experimental traumatic brain injury (TBI) diffusion tensor imaging (DTI) or histologic studies that might miss more widespread damage, when compared to the whole brain, statistically robust method of tract-based analysis used more routinely in clinical research. To determine the extent of DTI changes in this model, we acquired in vivo DTI data before and at 1 and 4weeks after CCI injury in 17 adult male rats and analyzed parametric maps of fractional anisotropy (FA), axial, radial, and mean diffusivity (AD, RD, MD), tensor mode (MO), and fiber tract density (FTD) using tract-based spatial statistics. Contusion volume was used as a surrogate marker of injury severity and as a covariate for investigating severity dependence of the data. Mean fiber tract length was also computed from seeds in the cortical spinal tract regions. In parallel experiments (n=3–5/group), we investigated corpus callosum neurofilaments and demyelination using immunohistochemistry (IHC) at 3days and 6weeks, callosal tract patency using dual-label retrograde tract tracing at 5weeks, and the contribution of gliosis to DTI parameter maps using GFAP IHC at 4weeks post-injury. The data show widespread ipsilateral regions of significantly reduced FA at 1week post-injury, driven by temporally changing values of AD, RD, and MD that persist to 4weeks. Demyelination, retrograde label tract loss, and reductions in MO (tract degeneration) and FTD were shown to underpin these data. Significant FA increases occurred in subcortical and corticospinal tract regions that were spatially distinct from regions of FA decrease, grossly affected gliotic areas, and MO changes. However, there was good spatial correspondence between regions of increased FA and areas of increased FTD and mean fiber length. We discuss these widespread changes in DTI parameters in terms of axonal degeneration and potential reorganization, with reference to a resting state fMRI companion paper (Harris et al., 2016, Exp. Neurol. 227:124–138) that demonstrated altered functional connectivity data acquired from the same rats used in this study.

From Online Motivations to Ad Clicks and to Behavioral Intentions: An Empirical Study of Consumer Response to Social Media Advertising

Marketers increasingly use social media advertising to promote their products and services. In particular, display ads have a prominent presence accompanying various social media feeds. This study aims to develop an understanding of how consumer online motivations (connection vs. consumption) lead to ad clicks on social media, which in turn affect behavioral intentions. A research model is developed to delineate two processes: First, the effects of motivations on ad clicks via perceived entertainment and informativeness values of ads, in which the mediating role of perceived congruity between ad and media content is proposed, too; second, the effect of ad clicks on behavioral intentions to purchase and spread positive word of mouth. The model was tested and confirmed with the online survey data of 613 social media users. Practical and theoretical implications are discussed.

Non-destructive Assessment of Highbush Blueberry Fruit Maturity Parameters and Anthocyanins by Using a Visible/Near Infrared (vis/NIR) Spectroscopy Device: A Preliminary Approach

We evaluate the use of a portable and non-invasive technology based on visible and near infrared (vis/NIR) spectroscopy (Cherry-Meter) for monitoring fruit maturity parameters and anthocyanins in two highbush blueberry (Vaccinium corymbosum L.) cultivars (Misty and Sharpblue). This device measures an Index of Absorbance Difference (I AD ), which showed high correlations with fruit quality parameters in other fruit crops. We found positive but differential correlations between I AD values and fruit anthocyanins, which was higher for Misty (r = 0.970, p≤0.01) than for Sharpblue (r = 0.714, p>0.05). Interestingly, Cherry-Meter measurements were also correlated with solid soluble concentrations (r = 0.685, p≤0.01) and fruit firmness (r = -0.714, p≤0.01), but only in Sharpblue. For both cultivars, I AD values were also significantly (p≤0.01) related with fruit FW (0.447 for Sharpblue and 0.559 for Misty). The High Performance Liquid Chromatography (HPLC) data indicated that I AD variations were associated with significant changes in single berry anthocyanidins levels. These findings are the first approach, highlighting the potentialities of Cherry-Meter for the non-destructive assessment of fruit maturity and anthocyanidin profile in blueberries.

Histogram Analysis of Diffusion Tensor Imaging Parameters in Pediatric Cerebellar Tumors.

Apparent diffusion coefficient (ADC) values have been shown to assist in differentiating cerebellar pilocytic astrocytomas and medulloblastomas. Previous studies have applied only ADC measurements and calculated the mean/median values. Here we investigated the value of diffusion tensor imaging (DTI) histogram characteristics of the entire tumor for differentiation of cerebellar pilocytic astrocytomas and medulloblastomas. Presurgical DTI data were analyzed with a region of interest (ROI) approach to include the entire tumor. For each tumor, histogram-derived metrics including the 25th percentile, 75th percentile, and skewness were calculated for fractional anisotropy (FA) and mean (MD), axial (AD), and radial (RD) diffusivity. The histogram metrics were used as primary predictors of interest in a logistic regression model. Statistical significance levels were set at p < .01. The study population included 17 children with pilocytic astrocytoma and 16 with medulloblastoma (mean age, 9.21 ± 5.18 years and 7.66 ± 4.97 years, respectively). Compared to children with medulloblastoma, children with pilocytic astrocytoma showed higher MD (P = .003 and P = .008), AD (P = .004 and P = .007), and RD (P = .003 and P = .009) values for the 25th and 75th percentile. In addition, histogram skewness showed statistically significant differences for MD between low- and high-grade tumors (P = .008). The 25th percentile for MD yields the best results for the presurgical differentiation between pediatric cerebellar pilocytic astrocytomas and medulloblastomas. The analysis of other DTI metrics does not provide additional diagnostic value. Our study confirms the diagnostic value of the quantitative histogram analysis of DTI data in pediatric neuro-oncology.

Longitudinal changes in the DTI measures, anti-GFAP expression and levels of serum inflammatory cytokines following mild traumatic brain injury

The majority of human mild traumatic brain injuries (mTBI; 70%) lack radiological evidence of injury, yet may present long term cognitive, and behavioral dysfunctions. With the hypothesis of evident damaged neural tissue and immunological consequences during acute phase of mTBI, we used closed skull weight-drop TBI model to address human mTBI condition. Serum cytokines (TNF-α, IL-10) and glial fibrillary acidic protein (GFAP) expression were examined at day 0 (control, pre-injury), 4h, day 1, day 3 and day 5 post injury (PI). Diffusion tensor imaging (DTI) was performed at similar timepoints to identify neuroinflammation translation into imaging abnormalities and monitor injury progression. DTI indices including mean diffusivity (MD), radial diffusivity (RD), fractional anisotropy and axial diffusivity values were quantified from cortex (CTX), hippocampus and corpus callosum regions. One way ANOVA showed significant increase in TNF-α at 4h and IL-10 at day 1 PI as compared to control. GFAP+ cells were significantly increased at day 3 and day 5 as compared to control in CTX. Repeated measures ANOVA revealed significant decreases in MD, RD values in CTX at day 3 and day 5 as compared to day 0. A significant, inverse correlation was observed between cortical MD (r=−0.74, p=0.01), AD (r=−0.60, p=0.03) and RD (r=−0.72, p=0.01) values with mean GFAP+ cells in the cortical region. These findings suggest that mTBI leads to elevated cytokine expression and subsequent hypertrophy of astrocytic processes. The increased numbers of reactive glial cells contribute diffusion restrictions in the CNS leading to reduced MD and RD values. These findings are in line with the deficits and pathologies associated with clinical mTBI, and support the use of mTBI model to address pathology and therapeutic options.

Diffusion tensor imaging and tract-based spatial statistics analysis in Friedreich's ataxia patients.

Friedreich's ataxia (FRDA) is the most common hereditary ataxia and thinning of the cervical spinal cord is a consistent observation in Magnetic resonance imaging (MRI), although neuropathological examination in FRDA reveals neuronal loss in gray matter (GM) nuclei and degeneration of white matter (WM) tracts in the spinal cord, brainstem and cerebellum. Using diffusion-tensor (DTI) imaging and tract-based spatial statistics (TBSS) we tested the hypothesis that WM damage in FRDA is more extensive than previously described and probably involves normal-appearing WM. This transversal study included 21 genetically confirmed FRDA patients and seventeen healthy controls that underwent structural MRI of the brain on a 1.5 T scanner. We quantify the severity of ataxia using SARA scale. DTI was performed and diffusion data were analyzed using FMRIB's Diffusion Toolbox in FSL 4.1 in order to identify Fractional anisotropy (FA) decreases in specific brain regions and also the mean, radial and axial diffusivities (MD, RD, AD). The greatest decreases in FA were in the left superior cerebellar peduncle, left posterior thalamic radiation, major forceps, left inferior fronto-occipital fasciculus and corpus callosum and had a significance level of p<0.01. No significant correlation between FA, AD, MD and RD values and the clinical findings, SARA scores and genetic expansion was found. DTI and TBSS techniques clearly demonstrate the extensive cerebral and cerebellar involvement in FRDA, partially explaining the clinical phenotype of the disease. Further studies are needed with larger samples to correlate clinical, genetic findings and ataxia scores.

Causes and consequences of trust in direct-to-consumer prescription drug advertising

Direct-to-consumer prescription drug advertising (DTCA) is believed to empower consumers, but national surveys indicate declining trust in DTCA. Given the unique characteristics of this category, it is unclear what the likely consequences are of reduced trust in these ads. Furthermore, previous research is inadequate to discern the basis of trust in DTCA. To address this issue, a model of the antecedent and consequent factors connected to trust in DTCA was developed based on prior empirical findings and relevant theory. This paper presents survey findings testing the model. Results show trust is predicted by perceptions of mediated health information sources, advertising in general, pharmaceutical companies, and the perceived value and informativeness of prescription drug ads. Regarding outcomes, results were mixed for the relationship of trust with attention, attitudes, and behavioural intent. Overall, findings suggest trust plays a complex role in shaping consumer reactions to prescription drug ads.

REMOVAL OF 2,4 DICHLOROPHENOL FROM WASTEWATER ON COST-EFFECTIVE SORBENTS: KINETICS AND THERMODYNAMICS INVESTIGATIONS

Maximum removal (94 1.2%) of 2, 4 dichlorophenol (50 mg.dm-3) was achieved on silica with agitation of 4 hours, at pH 8 and 42 C. The positive enthalpy (.H) and negative free energy values (.G315K) suggested the endothermic and a spontaneous nature of sorption. The free energy of the process at all temperature was negative and increased with the increase in temperature. The values of free energy suggested a spontaneous process where the spontaneity decreased with the rise in temperature. Positive values of .S described the randomness and a greater stability of sorption process with no structural changes at the solid-solution interface during the sorption. The data was subjected to Freundlich and Langmuir isotherms and the values of qe (mg.g-1), K1,ads and K2,ads(min-1) demonstrated that pseudo first order model was not fit for process, whereas, the pseudo second order kinetic model was best to describe the kinetics of process. The Elovich model and Intra particle diffusion kinetic model graph were best to describe the kinetics for DCP. A comparative experimental data revealed that developed method might be employed for removal of DCP from the aqueous industrial effluents before discharging them into water bodies.

Impact of Mobile App Ad Characteristics on Ad Value and Ad Attitude

Impact of Mobile App Ad Characteristics on Ad Value and Ad Attitude

Evaluación de la relación suelo-planta en un sistema productivo de leche del altiplano Nariño, Colombia

The research was conducted in the Arrayanes farm, Catambuco village, Department of Narino, Colombia. The objective was to evaluate the soil relationship on the composition of Loliumhybridum grass in monoculture and the mixture of Dactylisglomerata, Holcuslanatus and Loliumsp grass. The monoculture soil indicators in upper, middle and lower areas showed differences (P 0.05) were observed when the analysis per period (wet-dry) was performed. In pasture in mixtures, the results were statistically different (P 0.05). The results for grass mixture, by area showed no differences (P>0.05) in RD and TP. The AD values for time and zone in monoculture and mixed pastures were 0.66 to 0.71 (g/cc), RD 2.06 to 2.32 (g/cc) and TP between 66 to 70.9%. In monoculture differences (P<0.05) were observed, in the recovery period (RP) and biomass production (BP), both by time and by area. However in grass mixture, the RP was different (P<0.05) between periods, but no differences were observed by area.The RP values by period and area ranged from 26 to 32 d, the BP went from 4.4 to 4.8 (kg/m) in monoculture, while in the mixed prairie RP ranged from 45 to 60 d and BP from 4.9 to 5.8 (kg/m). In the bromatological analysis differences were observed (P<0,05) only per region for the crude protein (CP), neutrall detergent fiber (NDF), acid detergent fiber (ADF), calcium (Ca), phosphorous (P) , magnesium (Mg), and total digestible nutrients (TDN) were observed both in the prairie in monoculture and in the mixture. The values obtained were: PC 25,2%; FDN 50,6%; FDA 25,1%; NDT 64,6% and 0,22%, 0,30%, 0,14% for Ca, P and Mg, Veterinaria y Zootecnia ISSN 2011-5415 Vol 8 No.1, enero junio de 2014 ©Universidad de Caldas 67

Study of Pyrazolo[3,4-d] pyrimidine Derivative as Corrosion Inhibitor on 904L stainless Steel in Molar H3PO4

The corrosion inhibition of stainless steel type 904 L SS with different concentrations (10 -3 -10 -6 M) of 1,5-diallyl-1H - pyrazolo[3,4-d] pyrimidine (DPP) in acid solutions was investigated by potentiostatic polarization measurements. The effect of temperature (298-353°K) on corrosion parameters was examined. The open circuit potential values in the presence and absence of DPP noted before and after experiments indicated the formation of passive film on the surface of the samples. It was found that corrosion potential (E corr ) increases with increasing DPP concentrations, while, corrosion current (i corr ) decreases. Inhibition efficiency of DPP in 1M H 3 PO 4 . The inhibitor functions through adsorption and follows languimir isotherm in the acid. Activation energy (E a ) for adsorption of DPP is calculated. The values of ΔG ads decreased (attained more negative values) with increasing temperature.

Thermal conductivity of the sedimentary-cover rocks of the West Siberian Plate in relation to their humidity and porosity

We analyze the results of measurements of the thermal conductivity, porosity, and permeability of Mesozoic sedimentary rocks from wells drilled in the northeast of the West Siberian Plate and in the Cis-Yenisei basin. The thermal conductivity was measured by a “Thermal-conductivity comparator”, and the porosity and permeability were determined using standard techniques. A total of 135 samples of dry rocks were studied for thermal conductivity (Ad). Ninety-two of them were then saturated with water, and their thermal conductivity was measured again. The average thermal conductivity of dry and water-saturated (Aw) sedimentary rocks is 1.8-2.0 W/m/K and 2.4-2.8 W/m/K, respectively. Porosity (Kpor) was measured for 95 samples, and permeability (Kperm), for 44 samples. Comparison of the results of measurements revealed stable linear correlations between the thermal conductivity of dry samples and Aw, Kpor, and Kperm. The established dependences are proposed for the express evaluation of the thermal (Aw from Ad and Kpor values) and structural (Kpor and Kperm from Ad values) properties of sedimentary rocks, though the revealed correlations need further refinement.

Complexity analysis of beat-to-beat skin-surface laser-Doppler signals in diabetic subjects

MotivationsThis study performed skin-surface laser-Doppler flowmetry (LDF) measurements with the aim of verifying if complexity analysis applied to the beat-to-beat LDF waveform index can be used to discriminate diabetic, prediabetic, and normoglycemic subjects. MethodsSixty-six subjects were assigned to three age-matched groups according to the results of oral glucose tolerance tests. Beat-to-beat analysis was performed on the pulsatile LDF waveform to obtain the pulse-to-mean ratio (AD) and pulse width (PW), and then approximate-entropy (ApEn) values for their 20-minute index sequences were calculated to evaluate the signal complexity. ResultsAD and PW did not differ significantly among the three study groups. ApEn values of AD and PW were significantly larger and marginally larger, respectively, in the diabetic group than in the prediabetic and normoglycemic groups. ConclusionThese results indicate the presence of significant differences in ApEn indexes among diabetic, prediabetic, and normoglycemic subjects. The presence of increased complexity in the LDF index sequence may be partly attributed to the adaptability of the microcirculatory regulatory activities or the impairment of the homeostasis mechanism of microcirculatory-blood-flow perfusion. The present findings may be pertinent to the early detection of the diabetes-induced impairment of this perfusion.

Alterations in white matter microstructures and cognitive dysfunctions in benign childhood epilepsy with centrotemporal spikes

Although benign childhood epilepsy with centrotemporal spikes (BECTS) is known to have good prognosis, patients often manifest neuropsychological impairments. This study aimed to investigate cognitive dysfunctions and their relationship with white matter microstructural changes in BECTS patients. Nineteen BECTS and 25 normal subjects aged 7-16 years were included. Neuropsychological performances were assessed by the Wechsler Intelligence Scale for Children III, executive function tests, verbal and visuospatial memory tests, the verbal fluency and Boston naming tests. Diffusion tensor imaging (DTI) was performed to measure the fractional anisotropy (FA), axial (AD), radial (RD), and mean diffusivities (MD). The voxel-wise tract-based spatial statistics and region of interest methods were used for DTI, and their correlations with cognitive variables were analyzed. Patients with BECTS had lower intelligence quotient (IQ) scores compared with those of the control group. Higher AD and MD values were found in the left superior longitudinal fasciculus, the retrolenticular part of the internal capsule, posterior thalamic radiation, sagittal stratum and the body of the corpus callosum in BECTS patients compared with controls. Lower performances in verbal IQ, freedom from distractibility and processing speed were correlated with higher AD in the left superior fronto-occipital fasciculus, and lower verbal IQ scores were correlated with decreased FA values in the splenium of the corpus callosum in these patients. White matter microstructural changes predominantly in the left hemisphere might contribute to their cognitive abnormalities especially verbal IQ in BECTS patients.

To Exclude or Not To Exclude: Further Examination of the Influence of White Matter Hyperintensities in Diffusion Tensor Imaging Research

White matter hyperintensities (WMHIs) visible on magnetic resonance imaging (MRI) are common in both healthy adults and in those with medical or psychiatric problems. A practical methodological issue for diffusion tensor imaging (DTI) researchers is whether to include, or exclude, participants from a control group who have WMHIs. The aim of this study was to compare the influence of WMHIs on whole-brain DTI in trauma control subjects. Participants were 48 patients (no-WMHIs, n=36; 2+WMHIs, n=12) prospectively recruited from the Emergency Department of Vancouver General Hospital (British Columbia, Canada). Participants completed an MRI brain scan at 6-8 weeks postinjury (mean, 47.3 days; standard deviation [SD], 6.2; range, 39-66). DTI was used to examine the integrity of white matter (WM) in 50 regions of the brain using measures of fractional anisotropy (FA), and mean (MD), radial (RD), and axial (AD) diffusivity. FA values that were >2 SDs below the mean, and MD, RD, and AD values that were >2 SDs above the mean, were classified as "abnormal scores" indicative of reduced WM integrity. In the entire sample, the 2+WMHI group had a greater number of abnormal FA, MD, and RD scores, compared to the no-WMHI group (p<0.015 and Cohen's d >0.82, indicating large to very large effect sizes, for all comparisons). When controlling for the effects of age using a matched-groups design, the 2+WMHI group still had a significantly greater number of abnormal FA, MD, and RD scores, compared to the no-WMHI group (all p<0.012, all d >0.89, large to very large effect sizes). Researchers should be aware that the inclusion or exclusion of subjects with incidental WMHIs will influence the results of DTI studies.

Widespread White Matter Alterations in Patients with End-Stage Renal Disease: A Voxelwise Diffusion Tensor Imaging Study

ESRD results in excessive accumulation of urea and toxic metabolites. Hemodialysis is usually performed to maintain health in patients with ESRD; however, it may cause silent white matter alterations in the earlier stages. Hence, this study aimed to perform voxelwise diffusion tensor analysis for global detection of subtle white matter alterations in patients with ESRD. Twenty-eight patients with ESRD and 25 age-matched control subjects were enrolled in this study. Each subject underwent CASI assessment and DTI. After spatial normalization of DTI images, voxelwise statistical analyses were performed to compare DTI parameters between the 2 groups. In patients with ESRD, AD, RD, and MD values were significantly increased, whereas the FA value was significantly decreased, mostly in the corpus callosum, bilateral sagittal stratum, and pons. Multiple regression analysis further revealed that both RD and MD were positively correlated with the duration of hemodialysis in the pons; however, no significant correlation was observed with FA. Negative correlations of RD and MD and a positive correlation of FA with the CASI score were observed in the corona radiata. We concluded that voxelwise DTI analysis is helpful in the detection of white matter alterations caused by hemodialysis.

Transgenic Mouse α- and β-Cardiac Myosins Containing the R403Q Mutation Show Isoform-dependent Transient Kinetic Differences

Familial hypertrophic cardiomyopathy (FHC) is a major cause of sudden cardiac death in young athletes. The discovery in 1990 that a point mutation at residue 403 (R403Q) in the β-myosin heavy chain (MHC) caused a severe form of FHC was the first of many demonstrations linking FHC to mutations in muscle proteins. A mouse model for FHC has been widely used to study the mechanochemical properties of mutated cardiac myosin, but mouse hearts express α-MHC, whereas the ventricles of larger mammals express predominantly β-MHC. To address the role of the isoform backbone on function, we generated a transgenic mouse in which the endogenous α-MHC was partially replaced with transgenically encoded β-MHC or α-MHC. A His6 tag was cloned at the N terminus, along with R403Q, to facilitate isolation of myosin subfragment 1 (S1). Stopped flow kinetics were used to measure the equilibrium constants and rates of nucleotide binding and release for the mouse S1 isoforms bound to actin. For the wild-type isoforms, we found that the affinity of MgADP for α-S1 (100 μM) is ~ 4-fold weaker than for β-S1 (25 μM). Correspondingly, the MgADP release rate for α-S1 (350 s(-1)) is ~3-fold greater than for β-S1 (120 s(-1)). Introducing the R403Q mutation caused only a minor reduction in kinetics for β-S1, but R403Q in α-S1 caused the ADP release rate to increase by 20% (430 s(-1)). These transient kinetic studies on mouse cardiac myosins provide strong evidence that the functional impact of an FHC mutation on myosin depends on the isoform backbone.